The present invention relates to a novel plasmid derived from Corynebacterium thermoaminogenes. The plasmid of the present invention can be utilized for improving coryneform bacteria, which are used for producing useful substances such as L-amino acids.
Amino acids, including L-glutamic acid and L-lysine, are produced by fermentative methods using the coryneform bacteria, which generally belong to the genus Brevibacterium, Corynebacterium or Microbacterium, or variant strains thereof (Amino Acid Fermentation, Gakkai Shuppan Center, pp.195-215, 1986).
In the industrial fermentative production of amino acids, besides improving the yield relative to saccharides, shortening the culture time, improving the amino acid concentration, and so forth, increasing the culture temperature is an important technical factor that increases the economical efficiency. That is, the culture is usually performed at an optimum fermentation temperature, which is 31.5° C. for Corynebacterium glutamicum. After the culture is started, heat is generated during the fermentation, and hence amino acid production is markedly reduced if this heat output is not removed. Therefore, cooling equipment is required in order to maintain the optimum temperature of the culture broth . On the other hand, if the culture temperature can be elevated, it is then possible to decrease the energy required for cooling and the cooling equipment can be reduced in size.
Among coryneform bacteria, Corynebacterium thermoaminogenes has been isolated as a coryneform bacterium that can grow in higher temperatures (Japanese Patent Application Laid-open (Kokai) No. 63-240779). Whereas growth of Corynebacterium glutamicum is markedly suppressed at 40° C., Corynebacterium thermoaminogenes can grow at a temperature of about 40° C. or higher, and is therefore suitable for high temperature fermentation.
Currently, reliability of DNA recombination techniques is steadily improving in Escherichia coli and coryneform bacteria. To improve microorganisms using DNA recombinant techniques, plasmids derived from microorganisms belonging to other species, genus, or broad host spectrum vectors are often used. However, plasmids native to the objective microorganism are generally used. In particular, when the optimum culture temperature for the objective microorganism to be improved is different from that of a microorganism of the same species or genus, it is preferable to use a plasmid native to the microorganism.
To date, plasmids derived from coryneform bacteria which have been obtained are pAM330 from Brevibacterium lactofermentum ATCC13869 (Japanese Patent Application Laid-open (Kokai) No. 58-67669), pBL1 from Brevibacterium lactofermentum ATCC21798 (Santamaria. R. et al., J. Gen. Microbiol., 130, pp.2237-2246, 1984), pHM1519 from Corynebacterium glutamicum ATCC13058 (Japanese Patent Application Laid-open (Kokai) No. 58-77895), pCG1 from Corynebacterium glutamicum ATCC31808 (Japanese Patent Application Laid-open (Kokai) No. 57-134500) and pGA1 from Corynebacterium glutamicum DSM58 (Japanese Patent Application Laid-open (Kokai) No. 9-2603011).
However, no plasmid native to Corynebacterium thermoaminogenes has been obtained at present.